The present invention relates to a push-button switch and, in particular, to a push-button switch having a simple structure incorporated with an overload protection function.
There are many kinds and types of push-button switches for various applications, such as one having a turn-on indicating lamp and one provided with an overload protection function. In terms of one having an overload protection function, there are also several kinds of protection principles or mechanisms being adopted. For example, both the blow-out of a fuse wire and the thermal deformation of a bimetal blade have ever been adopted as a trigger source for an overload protection. However, the fuse wire is not repetitive and thus its utility rate gradually decreases. As for the thermal bimetal blade, there are many kinds of mechanism, such as those disclosed in U.S. Pat. Nos. 5,786,742, 5,223,813, 4,937,548, 4,661,667, 4,931,762, 5,451,729, and 4,704,594.
For example in the U.S. Pat. No. 5,786,742, a so-called power-cutting member (72) used to alternatively set a set and a reset positions of a switch is disclosed. In that case, a bimetallic blade (75) is used to push a shaft seat (71) to trip and automatically reset a switch, and a button depresses contacts directly. Thus, if the button has jammed or pushed down by an external force, they would be kept in its conducting position even if overload occurs. Moreover, such a switch is not economical because of a use of up to four contacts to construct a conducting circuit. The possibility of generating an arc also increases. Furthermore, such a switch is troublesome to provide a wire connecting the bimetallic blade (75) with the conducting plate (74).
In U.S. Pat. No. 5,223,813, a bimetal beam (13), a common trip (17) actuated by the bimetal beam, a cam member (27), and a rocker actuator (33) are used to construct a circuit between contact members (7,1). In such a switch, the common trip (17) can result in a displacement in response to the deformation of the bimetal beam so as to release the cam member and to trip the switch. Moreover, neither a jamming of the rocker actuator nor a neglectful re-push on the switch after the event of overload has influence on its overload protection, because the rocker actuator indirectly actuates the common trip. However, such a switch is rather complicated. Moreover, since it needs a wire to be connected to its cantilever spring (5) and its bimetal beam (13), its assembly is also troublesome. Furthermore, a fail-action could possibly happen when overload occurs since the bimetal beam may be not able to simultaneously actuate the rocker actuator (33) and the common trip (17).
In U.S. Pat. No. 4,937,548, a circuit breaker that utilizes the deformation of a thermal actuator (76) to displace a lock lever (62) so as to release a bell crank lever operator (52) is disclosed. In this case, the actuator indirectly actuates a movable contact (86), and thus a jamming of the actuator and a re-push on the switch in case of overload can be avoided. However, such an arrangement is inconvenient to install an indicating lamp. In U.S. Pat. No. 4,661,667, a double-heart-shaped-shaped cam locking mechanism is used to obtain two locking-positions. However, such a switch lacks an overload protection function as well as a status-indicating function.
A main object of the present invention is to provide a push-button switch that has a simple structure and can obtain an exact protection action.
Another object of this invention is to provide a push-button switch having an overload protection mechanism capable of complying with any types of bimetal sheets without a need of high assembly accuracy.
To achieve the objects of this invention, this invention discloses a push-button switch with overload protection comprising:
a housing;
a conducting unit installed in the housing and including a first terminal, a second terminal, a first conducting leaf, and a flat bimetal sheet; the bimetal sheet having a movable working end, being able to deflect to an overlord position upon overload from a normal position, and a fixed opening end formed with a first and a second legs for respectively connecting with the first terminal and the first conducting leaf; the first conducting leaf being movable between a normal-open position in which the second leg is disconnected from the second terminal and a closed position in which the second leg is electrically connected to the second terminal; and
an actuating unit installed in the housing and including:
a stem to be actuated;
a positioning means includes a heart-shaped stepping recess and a locating cantilever for alternatively locating the stem in an upper reset position and a lower set position with respect to the housing;
a rocking lever pivotally supported on the stem along a pivoting axle and formed with a nose for depressing the conducting leaf and a resting tail opposite to the nose across the pivoting axle;
an enabling lever formed with a rotating center pivotally mounted on the housing, an engaging head for engaging with the working end of the bimetal sheet, and an enabling rest for supporting the resting tail and thus enabling the rocker lever; and
a lever reseating member for pushing the rocking lever into an idle position in which the resting tail can be supported by the enabling rest, during a reset course in which the stem moves from the set position to the reset position;
whereby the nose can depress and release the conducting leaf so as to make the latter move into the closed position and the normal-open position in response to the movement of the stem to its set position and its reset its reset position, respectively, in case the resting tail is supported by the enabling rest, and whereby the first conducting leaf can move to its normal-open position in response to a change of the bimetal sheet into its overload position.
According to the above structure, the switch could exactly trip in the event of overload, and one should manually reset the switch before turn it on again. Thus, it is easy to recognize whether an event of overload happens at an interval of power-off in the light of the position of the switch. Moreover, by virtue of the enabling lever, the positional relationship between the rocking lever and the bimetal sheet is easily accommodated.